Winter 2006 Issue

Beacon Monitoring with DSP

Monitoring for propagation beacons is far more effective with DSP, rather than just hoping for a strong signal burst to trip your squelch. . . .

By Gordon West, WB6NOA

When the DX and distant U.S. beacons begin to poke through the squelch circuit on 6 meters, you know the band is open somewhere in time to QSY up to 50.110 and 50.125 MHz to see who is on. Hundreds of 6-meter propagation beacons may be your first alert that the Magic Band is beginning to open!

On 2 meters and 125, 70, and 23 cm, propagation beacons help us keep track of tropospheric ducting opportunities. These VHF/UHF beacons begin to build slowly during a tropospheric duct and provide good clues as to the thickness of the duct, depending on which VHF and UHF bands are best bringing in the distant CW signals.

Propagation alerts over the internet are probably one of the best ways to hear when the bands are open, but for some of us, monitoring for propagation beacons is a passive way to hear the bands slowly or quickly open as the signal punches through squelch. Unfortunately, many new multiband VHF/UHF ham transceivers employ a squelch circuit that is gated either on or off by a transistor. Most of these “hard squelch” circuits also have slight histeresis, which means that any signal that triggers the squelch circuit open must be well above the background noise level. This unfortunate problem has caused many hams to miss a band opening and sometimes entire conversations just below the squelch-trip threshold point.

“I was listening for the Hawaii beacon on 144.170 MHz last Sunday, and I was careful to set the squelch just at the point where the background noise was squelched out. The radio was silent all day until a very noisy Ford drove by, briefly opening up the squelch circuit,” comments Bill Alber, WA6CAX. Much to his surprise, there was an ongoing conversation between Bay area distant hams and Paul, KH6HME, in Hawaii. Without squelch, he could hear the signals weak but readable, but with any squelch setting the weak signal was completely taken out.

Shown here left to right are the GAP in-line DSP system, the SGC noise-subtraction DSP speaker (on top of the Kenwood TS-790), and the Heil Sound speech-amplified DSP speaker. All three systems worked well for monitoring beacons.


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